In the case of building a ship or an offshore plant structure such as a drillship or the like in a shipyard, works are performed in a dock provided with a gantry crane or a medium/large crane.
FIG. 1 schematically shows a case where a supersized ship is built using a gantry crane G. The gantry crane G (usually called a “Goliath crane” in a work site) consists of a pair of vertical beams and a horizontal beam, and moves along rails R installed on the ground.
On the other hand, the medium/large crane has a rotatable boom. The medium/large crane is of a post type or is configured to move along rails R installed on the ground.
The gantry crane G or the medium/large crane lifts up a component manufactured in a component manufacturing factory and then transports the component to a necessary place where a ship or an offshore plant is built.
When building a supersized ship or an offshore plant having a weight of hundreds of thousands tons, it is necessary to simultaneously input several hundreds of workers or several thousands of workers to a work site.
For this purpose, as illustrated in FIG. 1, a lift L or stairs (not shown) for transporting workers to a work place is additionally installed on a lateral side of a ship S to be built.
However, the lift L of the related art illustrated in FIG. 1 is not capable of simultaneously transporting a large number of workers to a high work site. Since the lift L illustrated in FIG. 1 is a small-sized lift typically installed in a construction spot, only several workers can get on the lift L at one time.
Thus, a great deal of time is required in deploying several hundreds of workers or several thousands of workers to a high work site. As a result, the actual work time is reduced and the productivity is deteriorated.
In the case where workers move up and down through stairs, there is a high risk that a slip accident occurs when rain or snow falls.
Furthermore, in the case of using the lift or the stairs, a great deal of time is wasted during the commuting time or before and after the lunch time.
In reality, it is sometimes the case that, when building a large ship, more than one hour is required in completely deploying workers to a high work site.
In order to solve the problems noted above, it may be thinkable to install a plurality of lifts L. In this case, the lift installation cost increases. Moreover, the problems cannot be completely solved by merely installing additional lifts.
Furthermore, the lift transportation method of the related art is not capable of appropriately coping with a situation that there is a need to rapidly evacuate a large number of workers to the ground in the case of occurrence of a fire or a safety accident. Thus, if a fire or an explosion accident occurs in a building site of a large ship or an offshore plant, this may lead to big tragedy.
In addition, the lift of the related art is designed to merely transport workers and is not capable of transporting heavy materials or work vehicles such as a forklift truck and the like.
If the weight of a material exceeds the load capacity of a lift (e.g., about 1 ton), it is necessary to lift up the material using a crane. In this case, there is a need to employ a ground worker, a crane driver and a sky worker.
Under a windy or bad weather condition, it is difficult to perform a lift work using a crane. In the case of performing a lift work using a crane, the lift work is time-consuming and the risk of a safety accident is high.
Typically, a crane used in a shipyard has a height of several tens meters. It is therefore difficult for a crane driver to visually grasp a ground situation. Thus, the crane driver has to operate the crane while communicating with a ground worker using a walkie-talkie. In this process, there is a high risk of occurrence of an accident.
Moreover, the lift L of the related art is installed in the sky and, therefore, has a high risk of occurrence of a safety accident. The lift L is classified into a dangerous machine under the industrial safety regulations which prescribe that a safety guard shall get on a lift to operate the lift in a construction site.